tools/dm_restrict: Unshare mount and IPC namespaces on Linux

QEMU running under Xen doesn't need mount or IPC functionality.
Create and enter separate namespaces for each of these before
executing QEMU, so that in the event that other restrictions fail, the
process won't be able to even name system mount points or exsting
non-file-based IPC descriptors to attempt to attack them.

Unsharing is something a process can only do to itself (it would
seem); so add an os-specific "dm_preexec_restrict()" hook just before
we exec() the device model.

Also add checks to depriv-process-checker.sh to verify that dm is
running in a new namespace (or at least, a different one than the
caller).

Suggested-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
---
Changes since v4:
- Fix function prototype for netbsd code

Changes since v3:
- Fix some more style issues

Changes since v2:
- Return an error rather than calling exit()
- Use LOGE() and print to the current stderr fd, rather than
  printing to the new stderr fd via write()
- Use r for external return values rather than rc.

CC: Ian Jackson <ian.jackson@citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Anthony Perard <anthony.perard@citrix.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/docs/designs/qemu-deprivilege.md b/docs/designs/qemu-deprivilege.md
index 82b0e15d81..65754ba6ee 100644
--- a/docs/designs/qemu-deprivilege.md
+++ b/docs/designs/qemu-deprivilege.md
@@ -76,12 +76,6 @@ Then adds the following to the qemu command-line:
 	
 '''Tested''': Not tested
 
-## Restrictions / improvements still to do
-
-This lists potential restrictions still to do.  It is meant to be
-listed in order of ease of implementation, with low-hanging fruit
-first.
-
 ## Namespaces for unused functionality (Linux only)
 
 '''Description''': QEMU doesn't use the functionality associated with
@@ -109,6 +103,12 @@ call:
 
 [qemu-namespaces]: https://lists.gnu.org/archive/html/qemu-devel/2017-10/msg04723.html
 
+# Restrictions / improvements still to do
+
+This lists potential restrictions still to do.  It is meant to be
+listed in order of ease of implementation, with low-hanging fruit
+first.
+
 ### Basic RLIMITs
 
 '''Description''': A number of limits on the resources that a given